diff --git a/ChangeLog b/ChangeLog
index 43365c401f..7b9b116700 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Jul  9 01:17:57 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (bigrsh_bang): Fix bignum digits overrun.
+
 Tue Jul  9 00:46:22 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (biglsh_bang): Fix bignum digits under-run.
diff --git a/bignum.c b/bignum.c
index c93061d44f..5918cefb7e 100644
--- a/bignum.c
+++ b/bignum.c
@@ -4452,11 +4452,11 @@ bigrsh_bang(BDIGIT* xds, long xn, unsigned long shift)
     i = 0;
     zds = xds + s1;
     num = *zds++>>s2;
-    do {
+    while (i < xn - s1 - 1) {
 	xds[i++] = BIGLO(*zds<<s3) | num;
 	num = *zds++>>s2;
     }
-    while (i < xn - s1 - 1);
+    assert(i < xn);
     xds[i] = num;
     MEMZERO(xds + xn - s1, BDIGIT, s1);
 }